Elastomeric yarns



United States Patent US. Cl. 57153 6 Claims ABSTRACT OF THE DISCLOSURE The surface friction of a synthetic elastomeric filament is reduced by applying a thin coating of a synthetic fibreforming, non-elastomeric polymer which does not affect the mechanical properties of the filament. The coating is formed in situ by treating the filament with polymerforming ingredients.

The present invention relates to synthetic elastomeric yarns, for example, those described in British patent specification No. 870,292 or US. patent specification No. 3,097,192, British patent specification No. 962,186, Belgian patent specification Nos. 637,982 and 659,935, and French patent specification No. 1,368,153.

The manufacture and processing of synthetic elastomeric yarns frequently runs into difiiculties resulting from a surface tackiness which is inherent in many yarns. This tackiness may make removal of a yarn from a package difficult or impossible and also results in the development of a high coefficient of friction between the yarn and surfaces, such as guides, over which the yarn may have to pass in processing. One suggestion to alleviate these problems, to some extent at least, is to dust the yarn with an inert powder such as talc before winding the yarn onto a package.

One characteristic of some elastomeric yarns is the stick-and-jump behavior which they exhibit when a bare yarn is pulled over itself.

In the context of the present specification the expression pulled over itself means that a length of yarn was pulled over a bobbin of the same yarn with an angle of wrap such that the pulled yarn contacted a quarter of the bobbin circumference.

We have now found that a thin coating of certain polymers can be applied to bare elastomeric yarns, without substantially impairing the properties of the latter, which overcomes the problems associated with tackiness and imparts increased lubricity to the elastomeric yarn.

Accordingly therefore the present invention provides a synthetic elastomeric yarn having reduced surface friction comprising at least one elastomeric filament coated with a synthetic fibre-forming non-elastomeric polymer. Preferably the coated filaments are in the drawn condition.

The term elastomeric implies that the filaments have rubber-like characteristics, for example it can be repeatedly stretched to about 150% or more of its original length and thereafter return with force to approximately its original length.

Polymers suitable for synthetic elastomeric yarn formation are well known. Of special interest are the segmented condensation polymers, for example, those obtainable by reaction between a polyester (say co-polyester) a diol or diamine and an aromatic or aliphatic diisocyanate (which latter may be used in molar excess). The polymer substance that forms the coating may be selected from a variety of known polymer types, for example, polyamides, polyureas, polyesters, polysulphonamides and polyurethanes which, for convenience, are hereinafter referred to as hard polymers and is preferably formed on the running yarn surface by reaction between polymer forming ingredients dissolved in substantially immiscible solvents, the polymer-forming reaction then being the same as the reaction that takes place in the method of polymerisation known as interfacial polymerisation (see Journal of Polymer Science, volume 40, pp. 289-416). In general, for a commercially attractive method, rapid surface polymer-formingreaction will be desired and, although suitable monomers which are fast reacting at room temperature are well known (see for example, U.S. patent specification No. 2,708,617), some examples are quoted hereinafter. Solvents, that do not destroy or have an unduly harmful effect on the particular elastomeric yarn being coated should be selected for the polymer forming ingredients. It is beneficial to the achievement of a more durable and tenaciously held coating for the surface portions of the elastomeric yarns which are to be coated to be in a swollen condition by virtue of solvent action, since such swelling facilitates anchorage of the coating polymer. The solvent containing the polymer forming ingredient first applied to the surface portions of the elastomeric yarn may effect such swelling action. Selection of the best solvent for any particular combination of base elastomer and polymer forming ingredient will frequently be a matter for trial and error, since different solvent types will be expected to interact with different elastomers to different extents. Some examples of suitable solvents used with particular elastomers and surface polymers are given hereinafter. The elastomeric yarn may be wet-spun, dry-spun or melt-spun. The process of the invention can conveniently be carried out by effecting the surface coating reaction on the yarn before it is wound up on the package.

A simple and effective way of applying a solution of a polymer forming ingredient to a running elastomeric filament is to cause the filament to pass in contact with the solution at one end of a capillary which communicates at its other end with a constant head reservoir ofthe solution. Keeping the filament in contact with the solution at the end of the capillary is facilitated by channelling or forming a groove in the member (say glass rod) in which the capillary is formed where the capillary terminates. A filament passing through such a channel or groove is confined laterally and spreading of the applied solution to all sides of the running yarn is encouraged. A solution of the second polymer forming ingredient may be applied to the filament via a second capillary.

The yarns formed by the method of the invention are useful as alternatives, for example, to the traditional wrapped sheath and core type of elastomeric yarn; they may be of low denier; and they are to be preferred to bare elastomeric yarns on account of the reduced tackiness and easier handling on processing equipment which they exhibit. The surface tackiness and friction of the polymercoated elastomeric yarns produced by the method of the invention are commonly lower than those of, for example, talc-dusted elastomeric yarns.

The yarn made by the method of invention can be formed into knitted articles such as surgical hose.

It has been found that even a very thin surface coating of hard polymer (say one increasing the denier of the elastomeric yarn by less than 1 percent) is capable of markedly improving the surface properties of elastomeric yarns. Thick coatings are less desirable since elastomeric properties of the yarn may be impaired and some of the coating may rub or flake off.

The elastomeric yarn may be drawn before or after having been given a surface coating and in some cases it has been observed that elastomeric yarns drawn, after coating with a hard polymer, crimp spontaneously in the relaxed condition. Such spontaneous crimping has also been observed in undrawn yarn in cases where a thick coating of hard polymer has been applied to an as-spun elastomeric yarn between spinning and initial wind-up.

Spinning finish or other surface coating material applied to the elastomeric yarn prior to coating should be removed before effecting the polymer-forming reaction at the surface of the elastomeric yarn since such material may interfere with the formation of a tenaciously-held polymer coating.

A surface coating of a polyamide may be formed by reaction of a diacid chloride (dissolved in a dry organic solvent) with a diamine (dissolved in water) in the presence of an acid acceptor (for example sodium carbonate or excess diamine). Suitable acid chlorides are adipyl, suberyl, sebacyl, dodecanoyl, terephthalyl and isophthalyl chlorides. Suitable diamines are primary and secondary aliphatic or arylaliphatic diamines, primary and secondary aliphatic or arylaliphatic diamines, primary diamines (for example, tetramethylene diamine, hexamethylene diamine, p-xylylene diamine, m-xylylene diamine, and 1.4-bis (amino methyl) cyclohexane) being preferred since they react fastest.

Surface coatings of polysulphonamides may be formed by reactions equivalent to the above-mentioned polyamideforming reactions (the disulphonyl chloride replacing the di-carboxylic acid chloride).

A surface coating of a polyurea may be formed by reaction of a diisocyanate (preferably an aliphatic diiso- :yanate since polyureas derived from aromatic diiso- :yanates generally discolour badly on exposure to light) with a diamine, the diisocyanate being dissolved in an organic solvent and the diamine being dissolved in water. Suitable diisocyanates are tetramethylene diisocyanate, hexamethylene diisocyanate, and p-xylylene diisocyanate.

Surface coatings of polyesters may be formed by reaction of diacid chlorides, such as those listed hereinbefore, with dihydroxy benzenes, such as hydro-quinone or bis-phenol A, in the presence of an acid acceptor, such as sodium hydroxide.

A suitable solvent for acid chlorides is methylene chloride which causes surface swelling of polyester urethane elastomers. Methylene chloride is also suitable as a solvent for aliphatic diisocyanates when coating polyester urethane elastomers with polyureas. Chloroform has been observed to cause a greater degree of swelling of polyester urethane elastomers with attendant greater modification of the elastic properties of the base elastomer and thicker deposition of hard polymer.

The following examples illustrate but do not limit the present invention.

EXAMPLE 1 2708 parts of a hydroxy-terrninated copolyester derived from ethylene glycol and 1,3-dihydroxy-2,2-dimethyl propane in the molar proportion of 7 to 3 and adipic acid, and having a molecular weight of 1760 were thoroughly mixed with 388 parts of 1,4- butane diol and heated to a temperature of 100 C. under an atmosphere of dry nitrogen. 970 parts of hexamethylene diisocyanate were then added to this melt over a period of 2 hours, while stirring continuously. During this period the temperature was raised gradually from 100 C. to 190 C. (When 96% of the diisocyanate had been added the temperature was 160 C. and the remaining 4% of the diisocyanate was added very slowly while the temperature was raised to the final reading of 190 C). The total of the diiso- :yanate introduced represented 98.5% of the stoichiometric quantity required by calculation based on the total hydroxyl equivalents of the polyester and butane :liol. The polyesterurethane thus obtained has a meltviscosity of 3500 poises at a temperature of 170 C. and was extruded from the polymerisation vessel as a lace of inch in diameter which was solidified in cold 'water. The lace was dried and cut into 4; inch long beads. The polyester urethane polymer had an inherent viscosity of 0.89 and a Vicat softening point of 143 C.

The polyester urethane was melt-spun at 190 C. through a 5-hole spinneret under a pressure of 250 psi. The extrusion rate was 1.7 gm./min. and the wind-up speed was 200 ft./min. The filaments were allowed to converge to form a yarn approximately 2 ft. below the spinneret. The yarn was guided into a groove formed across the end of a capillary tube (the capillary diameter was 1 .mm.) to which was supplied a 0.1 molar solution of sebacyl chloride in methylene chloride from a constant level reservoir. The yarn then passed along a second groove formed across the end of a second capillary tube which was placed about 1 ft. below the first capillary tube and to which was supplied from a second constant level reservoir an aqueous solution containing 0.25 mole of hexamethylene diamine and 0.5 mole of sodium carbonate per litre. The yarn then passed around a small godet at a angle of wrap and while running horizontally was washed with a running solution of 0.5 molar aqueous acetic acid and wound up.

The coated elastomeric yarn had an opaque appearance whereas the bare elastomeric yarn was glossy and transparent. The coated yarn could be pulled over itself without showing the stick-and-jump behaviour exhibited by the bare elastomeric yarn when pulled over itself.

The mechanical properties of the bare and coated elas- Elastic recovery is determined using an Instron tensile tester. A 5 cm. length of the yarn is extended by at a rate of 100% per minute whereupon the yarn is promptly allowed to recover at a rate of 100% per minute and the elastic recovery is expressed as the immediate percentage return to original length.

Work recovery is determined using an Instron tensile tester and is the ratio of the work recovered from a yarn specimen when the stress is released to the work expended when the specimen is elongated (under the same conditions as for elastic recovery determination). It is calculated as the ratio of the area under the stress-strain curve on the recovery cycle to the area under the stress-strain curve on the elongation cycle and expressed'as a percentage.

The friction measurements were made in the following way. The yarn was passed around a cylindrical pin at a small angle of wrap (around 30) and at a linear speed of travel of 15 feet per minute. The tensions in the yarn approaching and leaving the pin were determined using suitable tensiometers. The tension in yarn approaching the pin was arranged to be approximately 1 gram weight. The cylindrical pin was mounted at the upper end of a vertical cantilever which was fitted with a transducer permitting measurement of cantilever difference in a horizontal direction. Previous calibration of the cantilever displacement enabled the tension in the yarn leaving the pin to be determined, and hence the percentage increase in tension on passing around the pin (AT) and the dynamic coefficient of friction (,u) to be calculated. Two different cylindrical pins were used in the tests, the one having a polished chrome surface and the other having a Sintox surface. (Sintox is a trade name for a brand of ceramic material.)

EXAMPLE 2 A polyester urethane polymer was prepared and meltspun as described in Example 1 and the following reagents were applied to the yarn from grooved capillaries also as described in Example 1.

1st Capillary: 1.0 molar solution of hexamethylene diisocyanate in methylene chloride.

2nd Capillary: 1.0 molar solution of hexamethylene diamine in water.

The yarn was finally washed with 0.5 molar aqueous acetic acid and wound up.

With the higher concentrations of reagents as compared to those used in Example 1, a thicker coating was formed on the yarn some of which could be rubbed off but leaving, even so, an effective coating intact. Samples of the bare as-spun elastomeric yarn and the polymer coated elastomeric yarn were rewound and a commercial spinning finish applied. The samples were drawn to 3 times their original lengths and it was observed that the yarn having a polyurea coating crimped spontaneously, behaving as a conjugate filament. The following Table 2 includes measurements of surface friction which demonstrate that the coated yarn has a lower surface friction than the bare elastomeric yarn whether or not a commercial spinning finish had been applied.

Polyurethane polymer prepared as described in Example 1 was melt-spun by a screw extruder at a wind-up speed of 2000 'ft./min. 1.0 molar solutions of hexamethylene diisocyanate (HMDI) made up in two different solvents were applied to two different samples of the yarn, followed in each case by application of a 1.0 molar solution of hexamethylene diamine in water. The solutions were applied as in Example 1. Thereafter the yarn samples were washed with acetic acid applied from a roller, and a commercial spinning finish was then applied. The properties of the resultant yarns are each compared in the following Table 3 with the properties of a sample of the as-spun elastomeric yarn which had not been coated with polyurea.

TAB LE 3 Solvent for HMDI Bare Yarn properties elastorner CH2C12 CHCl;

Recovery from 100% extension:

Elastic recovery (percent) 90 90 90 Work recovery (percent) 46 45 42 It can be seen from Table 3 that the yarn which had had the HMDI applied dissolved in methylene chloride had major properties not significantly different from those of the bare elastomeric yarn. It would appear however that chloroform, being a more powerful swelling agent for the polyester urethane elastomer, has allowed This example illustrates that coating of an elastomeric yarn by a polymeric material can be performed during a re-winding process.

A finish-free sample of the bare polyurethane elastomeric yarn obtained as described in Example 1 was unwound at 200 ft./min. and treated with a 1.0 molar solution of hexamethylene diisocyanate in methylene chloride followed by a 1.0 molar aqueous solution of hexamethylene diamine, both solutions being applied from grooved capillaries as described in Example 1. The yarn was washed with running water as it passed over a roller and was wound up at 240 ft./min. A second sample of the bare elastomeric yarn was re-wound similarly but receiving only the water wash. The properties of the coated and uncoated yarns are compared in the following Table 4.

TABLE 4 Polyurea Yarn properties Bare yarn coated yarn Denier 138 139 Tenacity (g.p.d.) 0. 732 0. 818 Extension at break percent) 327 308 Recovery from 100 0 extension:

Elastic recovery (percent)- 92 95 Work recovery (percent) 47 51 Friction values:

On polished chrome:

AT (percent) 122 23 p 1. 83 0. 47 On Sintoxz AT (percent) 31 17. 5 u 0. 62 0. 73

Although the thickness of the coating is very small (as indicated by the small difference in denier) and the major mechanical properties are only slightly affected by the coating, the reduction in surface friction is very marked.

EXAMPLE 5 V period of 1 hour while stirring continuously following the procedure essentially as described in Example 1. The final temperature of polymerisation was C. Vacuum was applied to the melt for 5 minutes in order to remove gaseous bubbles. Stirring was then stopped and the apparatus brought to atmospheric pressure by the introduction of dry nitrogen. The stirrer was pulled out of the melt and the polymer allowed to cool. The polymerisation tube was shattered in liquid nitrogen and the polymer separated from the glass. The frozen polymer had an inherent viscosity of 1.54 (in-o-chlorophenol as a 0.5% by weight solution) and a Vicat softening point of 112 C.

The polymer was melt-spun at 210 C. through a 5-hole spinneret, using a pressure of 400 pounds per square inch. The extrusion rate was 1.6 grams per minute and the wind-up speed 200 feet per minute.

To the converged running filaments beneath the spinneret was applied from a 1st grooved capillary a 0.5 molar solution of hexamethylene diisocyanate in carbon tetrachloride, then from a second grooved capillary a 0.5

molar aqueous solution of hexamethylene diamine followed by a 0.5 molar acetic acid wash and commercial spinning finish. The monomer solutions were applied to the capillary as described in Example 1.

Unlike the polyurea-coated yarn, a sample of the elasto- W in Example 2 were applied to the running yarn below i yam to Whlch no i E i hadlbeen apthe spinneret. The polyurea thus formed on the yarn surphed l comma??? Spmnmg fi cou d face eliminated yarn tackiness, whereas the bare yarn Wound only wlth dlificulty fr,om Its package 7 was extremely tacky and had to be dusted with talcum The qp l POLYUIeaYCOated i bar powder at spinning to prevent coalescence on thepackalastomlsnc yams are gwelp m thfi Onowmg Table age. The properties of the polyurea coated yarn are com- TABLE 5 pared.with those of the'bare yarn having a talc dusting V g in the following Table 7.

Bare elasto- Polyurea- Yarn Properties meric yarn coated yarn TABLE 7 7 7 lenacity (g.p.d.) i V 9. 706 1. 04 s Talc dusted Polyurea- Extension at break (percent) 314 274 Yarn properties elastomeric yarn coated yarn Recovery from 100% extension: 5 V Elastic recovery (percent) 97 95 Tenacity (g.p.d.) ,0. 825 r 0.830 Work recovery (pereent). 63 5; Extension at break (percent) 760 812 On polished Chrome: Recovery from 100% extensio AT (percent) 234 27 Elastic recovery (percent). 98 V 7 p 2.84 0.54 'Workrecovery (percent) i 84 8 urf6ce f gissggixs alues (arbitrary units) AT (statesman... 60 27 1 EXAMPLE 8 W An N-alkylated copolyarnide elastomer was prepared as follows: 7 7 3 meaured pfiopertlels mpnstrate the l' i 958 parts of N,N'-diisobutyl hexamethyle ne diamine, 3.: e coating of ardpo ymerlc material on the sur ace 808 parts of Sebacic acid, 160 parts of naming Jr the elastomer 1n eliminatingsurface tackiness andredecanoiceracid 2712 parts of caprolactam 120 parts of C1112 substantlally y 'ff furface fnctlon' distilled water, 2.4 parts of orthophosphoric acid and i AM 0.8 parts of Silicolaps anti-foam were charged to a 3 gallon, vapour heated, agitated, stainless steel autoclave. 1830 parts of a hydroxy-terminated copolyester de- The autoclavewas heated to boiling point, purged with rived from ethylene glycol and propylene glycol in the steam to remove air and sealed (during the course of molar proportion of 7 to' 3 and adipic acid and having 50 minutes). Heating was further continued for 50 a. molecular weight of 1830 were reacted with 800 parts minutes by which time the temperature had reached 260 9f 'tp-i cyanato-phenyl) methane at 80 C. for 2 C. and the pressure had reached 180 p.sli. The pressure iours. To this prepolymer were added 180 parts f ,4 was reduced to atmospheric during a period of 50 minutes Jutane diol, the mixttire was then stirred vigorously whil the temperature rose to 290 C. whereupon the For a few minutes after which it was poured out into temperature was maintained at 290 C. for a further 40 in p Shallow Stainless Sled mould in p minutes. The pressure above the melt was then slowly and stored at 80 C. for 20 hours. The resultant polymerf" d d u til, after 65 minutes, a pressure of 1 mm. bad a Viscat Softening Point of and was melt-Spun" had been reached. The pressure was maintained at 1 it a temperature f 200 Cfu ing. a'p cs u e 0f for 20 minutes, after which the molten polymer through a 541016 p r t as described n the was extruded as a ribbon under nitrogen pressure, previous examples. 7 5 7 quenched, chipped while wet, and dried.

T0 the rimming Converged filaments below thfi Spinnerit The polymer had the following characteristics: was applied from a first capillary a 0.5 molar Solution of AEG F 06 73 7 sebacyl chloride in methylene chloride, and from a second 'A :apillary an aqueous solution containing 0.5 mole per IV 0 87 ,itre of hexamethylene diarnine and 0.5 mole per litre :if sodium carbonate. The polyamide coated'yarn 0b- 140 .ained was finally washed with a 0.5 molar aqueous solu- I.V=inherent viscosity; S.P.=Vicat softening point, the :ion of acetic acid and a commercial spinning finish aptemperature taken being the temperature at which the )lied. A sample of the elastomeric yarn which had rate of penetration, as determined on a penetrometer lot been coated with polyamide, but only with the essentially the same as that described by 'Edgar and Ellery ipinning finish, was tacky unlike the polyamide-coated in J.C.S,, reaches a maximum, yarn and could be unwound only with great difiiculty. The polymer was melt-spun at 193 C. under a pres- In the following Table 6 the properties of the polysure of 300' p.s.i. through a S-hole spinneret. Solutions amide coated yarn are compared with the properties of of sebacyl chloride in methylene chloride and hexarnethyl- :he non-polymer-coated yarn to which talcum powder ene diamine in water were applied, as a described in had been applied at spinning to prevent coalescence of =30 Example 6, to the running yarn below the spinneret and :he threadline on the bobbin. thereafter the polyamide=coated yarn was washed and a spinning finish applied. A sample of the yarn to which TABLE no polyamide coating had been applied was extremely Control and Polyamide tacky and could not be unwound from its package. The Pmpemes talc coated polyamide coating reduced the yarn tackiness and yarn lenacity (g.p.d.) 0.825 0.660 surface friction to the level achieved by talcum powder gggg g; gg g ggg f 3313133 application without substantially impairing the elastic Elastic recovery (percent) 98 97 properties of the yarn. Work recovery (percent) 84 86 7O EXAMPLE 9 The elastic properties of the polyamide coated and The elastomer of Example 8 was spun as described uncoated yarns are very similar and not impaired by in that example and solutions of the diisocyanate and the coating. On the other hand, the surface friction propthe diamine described in Example 2 were applied to :rties of the elastomeric yarn were greatly improved the yarn from capillaries as described in previous examby the polyamide coating. ples. The polyurea coated yarn was Washed and a spinning EXAMPLE 7 'A sample of elastomeric yarn described in Example 6 was spun under the same-conditions as described in Example' 6 and the polymer-forming reagents described finish applied. The polyurea coating again reduced the tackiness and improved the surface friction properties of the yarn to the level achieved by talcum powder application and as shown in the following Table 8 the elastic properties of the yarn were not impaired by coating the yarn with polyurea.

What I claim is:

1. A synthetic elastomeric yarn having reduced surface friction comprising at least one elastomeric filament coated with a synthetic fibre-forming non-elastomeric polymer which increases the denier of the elastomeric filament by less than 1%.

2. A yarn according to claim 1 consisting of at least one elastomeric filament in the drawn condition.

3. A yarn according to claim 2 wherein the elastomeric filament comprises the reaction product of a polyester or copolyestcr, a diol or diamine and an aromatic or aliphatic diisocyanate.

4. A yarn according to claim 2 wherein the nonelastomeric polymer is a polyamide, polyester, polyurea' polysulphonamide or polyurethane.

5. A yarn according to claim 1 possessing a potential crimp.

6. A synthetic elastomeric yarn comprising at least one elastomeric filament and a thin synthetic fibre-forming non-elastomeric polymer coating which increases the denier of the filament by less than 1%, said yarn exhibiting a lower surface friction than said filament and exhibiting substantially the same tenacity, extension at break, elastic recovery and work recovery as said filament.

References Cited UNITED STATES PATENTS 2,146,314 2/1939 Radford 57149 2,380,373 7/1945 Alderfer 57-163 XR 2,484,125 10/1949 Silvain 161175 XR 2,539,300 1/1951 Foster 16117S 2,953,839 9/1960 Kohrn et a1. 161175 3,216,852 11/1965 Goldberg 117139.5 XR 3,255,030 6/1966 Storti 117l39.5 X'R 3,296,063 1/1967 Chandler 117139.5 XR

JOHN PETRAKES, Primary Examiner U.S. C1.X.=R. 

